The invention relates to carburettors for internal combustion engines of the kind comprising a main fuel delivery circuit for normal running, opening into a venturi of an induction passage, and at least one auxiliary circuit for supplying to the engine a flow of air/fuel mixture for low speed and low-load operation of the engine, said circuits comprising mixture control means. The auxiliary circuit typically opens into the induction passage through an idling port disposed downstream of a throttle, and through at least one progression or by-pass port situated so as to pass from upstream to downstream of the throttle when the latter is opened from its minimum opening position.
In conventional carburettors, the fuel-air mixture control means are formed by calibrated restrictions which meter the fuel and/or air flows and are formed in jets. In recent carburettors, the restrictions are associated with or replaced by electromagnetically controlled valves energized by electric pulses width modulated by a control circuit, which may operate in closed loop and include a detector probe immersed in the exhaust gases of the engine.
The jets and/or electromagnetic valves are usually carried by the body of the carburettor and frequently screwed into tapped passages in the body. The main fuel jet is generally disposed in the float chamber of the carburettor; an air jet (or automaticity nozzle) for brining primary air for emulsifying the fuel supplied by the main circuit, is placed in the air intake of the carburettor. The idling jet is often screwed on the external part of the moulded body of the carburettor.
The distribution of the calibrated mixture control members at different points of the carburettor presents drawbacks. During assembly of carburettors for supplying different types of engines, calibrated members corresponding to different engines are inserted into carburettor bodies; it is necessary, to satisfy the needs, to have a supply of as many completed carburettors as there are types of engine, which results in excessive inventory costs.
Moreover, experience has shown, in conventional carburettors whose jet circuit comprises an emulsion well, flow fluctuations when the circuit is primed, as well as sudden changes in the fuel flow rate on full load, which changes are presumably due to the transmission of pressure pulses along the wall.
It is an object of the invention to provide a carburettor of simple and compact construction, of reduced cost, which is easily adaptable to different types of engine.
According to the invention, there is provided a carburettor of the above-defined kind in which the mixture control means are carried by a distribution block which may be handled as a whole, arranged and dimensioned for connection to the carburettor body in the induction passage in the vicinity of the venturi thereof.
Then the primary air-fuel mixture delivered by the main fuel supply circuits elaborated close to the place where it emerges into the venturi.
When said devices are calibrated restrictions of fixed cross-sectional flow area provided in jets, the latter may be easily placed in two support arms of the block.
It will be appreciated that such a construction is fairly different from those in which a carburation block constitutes an intermediate portion of the carburettor body (U.S. Pat. No. 3,284,066) and cannot be easily replaced with another one and there is no possibility to have an inventory of standard carburettor bodies in which appropriate blocks may be located.